1. Field of the Invention
The present invention relates to an anti-skid device for tired vehicle wheels and particularly to such anti-skid devices for use on tires when the tires are used on a snow-covered or frozen road.
2. Related Art Statement
Tire chains or snow chains are well known as one of anti-skid devices that are used on tires of an automotive vehicle so as to assure running stability of the vehicle when the vehicle is run on snow-covered road surfaces or frozen road surfaces. However, snow chains have a problem that it is time-consuming to mount and remove them on or from the tires. Furthermore, when used on normal or dry roads, snow chains wear the road surfaces on one hand while they are worn due to friction with the road surfaces on the other hand. Accordingly, drivers tend to hesitate about whether or not to use snow chains, except for such cases where it is likely that snow or ice road surface will continue a comparatively long distance.
In the above background, U.S. Pat. No. 4,576,214 to Preusker disclosed an anti-skid device which is more easily mounted on and removed from tired vehicle wheels so as to adapt the wheels to conditions of the road surface on which the vehicle is run.
The above anti-skid device includes (a) a setting disk secured to a vehicle wheel on which a tire is mounted; (b) a supporting disk removably secured to the setting disk; (c) a plurality of anti-skid arms extending radially outwardly from the supporting disk such that, with the supporting disk secured to the setting disk, bent-end portions of the anti-skid arms face a tread surface of the tire; (d) and a retaining ring for retaining the supporting disk to the setting disk by utilizing a bayonet-like locking mechanism so that the secured supporting disk will never come off the setting disk during running of the vehicle. In the anti-skid device, the retaining ring is rotated in one of opposite directions to secure the supporting disk to the setting disk and rotated in the other direction to remove the supporting disk from the setting disk.
The anti-skid arms of the above-indicated type anti-skid device are located in position on the tread surface of the tire by rotating the retaining ring in one direction relative to the setting disk fixed to the wheel rim so as to secure the supporting disk to the setting disk. On the other hand, the anti-skid arms are removed from the tread surface of the tire by first unlocking the bayonet-like locking between the retaining ring and the setting disk, and rotating the retaining ring in the other direction so as to remove the supporting disk from the setting disk. Accordingly, it is not required to jack up the vehicle body to mount the anti-skid device on, or remove the device from, the tire, or move the vehicle forward or backward. Thus, the prior art anti-skid device is more easily handled than conventional snow chains or tire chains.
However, the above anti-skid device suffers from problems of structural complexity and increased number of employed parts, because the supporting member is secured to the setting member by using the exclusive member, that is, retaining ring. Furthermore, an exclusive unlocking key is necessary for releasing the bayonet-like locking between the retaining ring and the setting disk.
Moreover, the prior art anti-skid device has a problem resulting from the fact that the diameter of a circle defined by the bent-end portions of the anti-skid arms is unchangeable. More specifically described, in the case where an anti-skid device whose anti-skid arms define a circle having a diameter greater than an outer diameter of the tire, is used for easier positioning of the anti-skid arms around the tire tread surface, an undesirable gap is provided between the bent-end portions of the anti-skid arms and the tire tread surface. Consequently, uncomfortable vibration is produced and transmitted to the vehicle body during running of the automotive vehicle. Moreover, due to that gap, the bent-end portions of the anti-skid arms are subjected to a comparatively high torsional stress during running of the vehicle, whereby the durability of the anti-skid arms is extremely deteriorated. Meanwhile, in the case where a circle defined by the bent-end portions of anti-skid arms is smaller than the outer diameter of the tire, another problem will occur that positioning of the bent-end portions of the anti-skid arms around the tire tread surface is difficult because of the unchangeable diameter of the circle defined by the bent-end portions of the anti-skid arms. It is further noted that uncomfortable vibration is also produced due to an undesirable gap which will grow little by little between the bent-end portions of the anti-skid arms and the tire tread surface as the tire is worn.